Printing-carriage back-spacing mechanism for teleprinters



Patented Oct. 6, 1970 Sheet MVENTORS A0050 9241/ Patented Oct. 6, 19703,532,205

v Patented Oct. 6,1970 3,532,205

Sheet 3 of 3 .JICS: 5 .IIEJU.

INVENTORJ H/OEO 02/440 PRllNTlNG-CARRHAGE BACKSPACHNG MECHANISM FORTELEPRKNTEEIS Conventional carriage mechanisms in teleprinter devicesare normally comprised of a carriage pulley belt for transmittingrotation from a drive wheel to a freely rotatable driven wheel. Thedrive wheel has secured thereto a ratchet for stepping the pulley belt.The printing typewheel assembly is mechanically secured to the pulleybelt for advancement therewith. A tension spring is coupled between theleft-hand end of the carriage typewheel assembly and a stationarysupport to normally bias the carriage typewheel assembly toward theleft. A shaft couples the drive pulley to a ratchet which is stepped inclockwise fashion in order to drive the pulley belt toward the right instepwise fashion against the pulling force of the tension spring. Aspace-suppression assembly is provided to prevent advancement of thecarriage typewheel assembly during a print operation.

The driving mechanism, commonly referred to as a carriage drive bail, ismounted for rocking rearwardly and forwardly to drive the carriageadvancement assembly which is comprised of a first pawl and a togglelinkage carrying a second pawl which is driven by the carriage drivebail to break at the knee of the toggle assembly and to remove itsassociated pawl from the ratchet while the first pawl holds the ratchetagainst counterclockwise rotation under the force of the tension spring.The carriage drive bail rocks in the reverse direction to straighten thetoggle assembly whose pawl engages the next notch in the ratchet,causing the ratchet to be driven stepwise by one incremental step toadvance the carriage typewheel assembly.

Backspace operation is performed by a third pawl pivotally coupled tothe connecting pin of the toggle assembly so as to be moved therewith.

All three pawls are provided with shoulders which confront a releaseplate which is operative to release the first and second pawls fromengagement with a tooth of the ratchet. The depth of the shoulderprovided on the third pawl is greater then the first two pawls so as tocause the third pawl to be maintained against the ratchet wheel. Anassembly is provided to prevent the release plate from being moved by anamount sufficient to drive the third pawl out of engagement with theratchet. When the release plate removes the first and second pawls fromthe ratchet, the tension spring through the carriage typewheel assemblyand the pulley rapidly urges the ratchet counterclockwise through anincremental angle to perform the backspace operation. The third pawlconfronts the shoulder positioned to the left of the third pawl toprevent the backspacing movement from stepping more than one space tothe left. The return of the release plate to its rest posi tion returnsthe first and second pawls back into engagement with the ratchet inreadiness for the performance of either a forward spacing or rearwardspacing operation under control of the operator.

The instant invention relates to teleprinters and other like typingdevices, and more particularly to a novel backspacing assembly which ischaracterized by its simplicity of design, and which may be readily andsimply added to already existing conventional teleprinter assemblies toafford such assemblies with the additional feature of performing abackspacing operation. There exist a number of applications in which itis advantageous to have a backspacing capability. For example, oneconventional teleprinter system is comprised of at least a pair ofteleprinters provided at remote locations for two-way transmission.Whenever an operator mistakenly depresses a key on the keyboard of histeleprinter in transmitting a message to a distant station, and,automatically, the teleprinter at the distant station prints themistaken character, numeral, or other symbol operated at the sendingstation, the necessity, therefore, arises for backspacing both the transmitting and the receiving printing carriages to the first mistypedcharacter position, and transmitting a delete code to the distantstation to strike the erroneously printed character. To accomplish thebackspacing operation, a variety of backspacing mechanism designs forincorporation into teleprinter systems have been proposed. The majorityof conventional backspacing mechanisms; have been found to be extremelybulky, complex mechanisms and quite unreliable in operation. it,therefore, becomes arprinciple object of the instant invention toprovide a simple, common new and improved printing carriage backspacingsystem that can be most easily and rapidly incorporated intoconventional teleprinter systems without backspacing facilities, andbeing of the type that the printing carriage is continuously urged by aspring under tension toward the left margin. inclusion of a backspacingfacility into teleprinters of this design can, therefore, be made with aminimum modification to existing parts, assemblies, and mechanismsincorporated therein.

One outstanding feature in the design of the instant invention whichenables the attainment of the above mentioned object, is theincorporation of a backspacing pawl performing a function substantiallysimilar to that performed by a check pawl, which is one element of apawl assembly consisting of a check pawl and a spacing pawl, in. such amanner that there may be produced a slight linear displacement betweenthe check pawl and the backspacing pawl with respect to the spacingratchet teeth, and further that all pawls may be released from theratchet upon reception of a carriage return code, whereas the check andspacing pawls will be released temporarily upon the reception of abackspace code so as to permit the ratchet to rotate in the backspacingdirection.

The instant invention is comprised of a backspacing pawl which ispivotally mounted to a pivotal pin forming the knee of a toggle assemblyfor the spacing pawl. The carriage operating bail causes the spacingpawl toggle assembly to collapse during movement in a first direction,thereby releasing the spacing pawl from the ratchet. The check pawl,however, remains in engagement with one tooth of the ratchet,restraining it from rotating in the backspacing" direction as a resultof release of the spacing pawl from the ratchet. The carriage bailassembly moves in the reverse direction, causing the spacing pawl toggleassembly to be extended, straightening the toggle assembly and advancingthe ratchet. by one tooth.

The carriage return operation is performed by releasing both thechecking and spacing pawls from the ratchet, placing the ratchet undercontrol of the tension spring which auto matically drives the typewheelcarriage to the extremely lefthand end of the teleprinter assembly. Thisfunction is obviously performed in conventional systems as one part ofthe carriage return line feed operation to cause printing to begin onthe next line. Release of the check and spacing pawls is performed by arockable release plate which, upon depression of the appropriatefunction key, drives the check and spacing pawls out of engagement withthe ratchet.

The operation of the release plate can be advantageously employed forthe backspacing operation by causing the release plate to drive thecheck and spacing pawls out of engagement with the ratchet, whilefailing to move through a sufficient angle to likewise drive thebackspacing pawl out of engagement with the ratchet. Once this functionis performed, the backspacing pawl abuts the next tooth of the ratchetas it attempts to move toward the left or toward the backspace directionunder control of the tension spring.

The release plate has its motion restrained by a mechanical linkagecoupled to the rockable release plate to restrain its movement as soonas the release plate has released both check and spacing pawls from theratchet, but before the release plate may remove the backspacing pawlfrom the ratchet. This control assembly may be added to already existingteleprinter structures with an absolute minimum of design modificationand primarily with simply the addition of the backspacing pawl and therelease plate restraining assembly.

The release plate restraining assembly is further fully compatible withsystem operation during a carriage return function by allowing thebackspacing pawl, as well as the check and spacing pawls, to be fullydisengaged from the ratchet in order to perform the carriage returnoperation.

It is, therefore, a major object of the instant invention to provide anovel device for use in teleprinters, and the like, to provide thecapability of a backspacing operation through the mechanics of abackspacing assembly which is simple and straightforward in design andwhich may be relatively easily and rapidly added to conventionaldevices.

Another object of the instant invention is to provide a novelbackspacing device for use in teleprinters, and the like, wherein thebackspacing pawl is added to an assembly comprised of a check pawl and acollapsible stepping pawl, and having a release plate capable ofreleasing all pawls from an associated ratchet to perform a carriagereturn operation, and for releasing only the check and spacing pawls tothe exclusion of the backspacing pawl to perform a backspacingoperation.

Yet a further object of the instant invention is to provide a novelbackspacing device for use in teleprinters, and the like, wherein thebackspacing pawl is added to an assembly comprised of a check pawl and acollapsible stepping pawl, and having a release plate capable ofreleasing all pawls from an associated ratchet to perform a carriagereturn operation, and for releasing only the check and spacing pawls tothe exclusion of the backspacing pawl to perform a backspacingoperation,

and further comprising a mechanism for controlling the movement of therelease plate so as to enable release of the check and spacing pawlsunder control of the release plate and to restrain the movement of therelease plate to prevent disengagement of the backspacing pawl from theratchet during an operation calling for backspacing movement.

The above as well as other objects will become apparent upon aconsideration of the accompanying description and drawing in which:

FIG. I is a perspective view of those portions of a teleprinter assemblywhich are significant from the viewpoint of understanding thebackspacing assembly of the instant invention.

FIG. la is an end view showing the essential part of the backspacingmechanism of FIG. 1.

FIGS. 2 through 6 are top plan views showing an essential part of thebackspacing mechanism in a predetermined format of operation so as toexplain the sequence of operations in order to understand the manner inwhich a teleprinter printing carriage is caused to perform a spacing,carriage return and backspacing operation. Each plan view is accompaniedby a simplified diagramatic representation, FIGS. 2a through 60respectively, showing the mode of operation and position of a pluralityof pawls relative to their associated ratchet wheel.

FIGS. 7 through 10 are side elevational views showing the portion of thefunction mechanism which are operative upon the reception of a backspacecode with the views 7 through 10 showing the mechanism in various stagesof operation in order to clarify the functional aspects of the instantinvention.

The backspacing mechanism of the instant invention may be advantageouslyadapted for use in a printing carriage assembly which is continuouslyplaced under spring tension toward the left margin of the device, andwhich is provided with a spacing mechanism functioning to space oradvance one character space (or pitch) against spring tension each timea character or space code is received. The printing carriage returns tothe left margin by spring tension upon receipt of a carriage return codein order to actuate the carriage return mechanism. In conventionalteleprinters, upon receipt of a carriage return code, both the spacingand backspacing pawl assemblies are released from the feed-wheel (i.e.,the spacing ratchet) through the aid of a carriage return mechanism.With the present backspacing mechanism, receipt of a backspace codefunctions to release only the spacing mechanism from the feed-wheel whena backspace code is received by incorporating a mechanism with thecarriage return mechanism to permit only the spacing mechanism to bereleased from the feed-wheel.

The backspacing mechanism, which is capable of remaining engaged withthe ratchet wheel, is installed with the conventional spacing mechanismas an integral part thereof while a simple mechanism for performing apartial operation of the carriage return mechanism when. a reception ofa backspace code is incorporated into the carriage return mechanism, isdesigned to perform a full release operation so as to release all pawlsfrom the feed or ratchet wheel upon the reception of a carriage returncode.

Briefly speaking, the backspacing mechanism, in accordance with theinstant invention, is an improved version of conventional backspacingmechanisms in that the printing carriage can be backspaced accurately byincorporating a simple mechanism into mechanisms already employed forexisting carriage return operations. FIGS. 1 and 1a illustrate apreferred embodiment of a backspacing mechanism which is incorporatedinto a teleprinter assembly of the stationary platen type.

The assembly shown therein is comprised of a spacing ratchet 2 arrangedin the lower left-hand corner. The shaft 5; on which ratchet 2 ismounted extends vertically upward to receive a driving sprocket orpulley SP rigidly secured to the upper end of the shaft 8,. A printingcarriage spacing belt 29 is entrained about the sprocket SP and a drivenpulley 50 which is rotatably mounted upon a shaft S installed on therighthand side of the teleprinter frame (only the topmost portion of theshaft S protruding through pulley 50 being shown in FIG. 1). Thefunction of the spacing belt 29 is to displace the carriage 28 which isrigidly secured thereto by clamping means 28a, either to the left or tothe right as required, and under control of the rotational movement ofsprocket SP.

The carriage 28 is maintained under tension by means of a large spring 1having a first end thereof secured to a righthand side frame member F bymeans of a screw or pin P, and which has its opposite end clamped at 280to the left-hand side of carriage 28. Spring I is entrained about apulley 44 positioned near ratchet wheel 2. Spring 1 is extended by anamount sufficient to cause it to place carriage 28 under tension andnormally bias it toward movement in the left-hand direction, as shown byarrow A. This spring force is transmitted through carriage 28 and belt29 to ratchet wheel 2, causing wheel 2 to have a normal tendency torotate in a counterclockwise direction about the longitudinal axis ofshaft 5,, as shown by arrow 60. The rotation of ratchet wheel 2,however, is blocked whenever any one of the pawls 4 through 6 engages anotch or tooth provided in ratchet 2.

The center portion of the illustration of FIG. 1 shows a code barassembly 27 comprised of a plurality of code bars, for example code bars26, 26a and 26b, equal in number to the number of code bits forming theteleprinter code. The code bars of group 27 are employed for the purposeof selecting the particular character to be typed or printed as setforth, for example, in copending, U.S. application Ser. No. 644,936filed June 7, 1967 now U.S. Pat. No. 3,431,943, and assigned to theassignee of the instant invention. When a code is received from thesending side teleprinter, the code received selectively operates codebars in the code bar group 27 of the receiving teleprinter which areactuated by the received code in order to select the appropriatecharacter or symbol to be typed.

Thus, code bars, for example code bars 26, 26a and 26b, which are equalin number to the Mark codes of a received signal contained in a code,move upwardly and to the left simultaneously in a manner suggested bythe above mentioned copending patent application.

A driving cam (not shown) rocks a drive arm 13 upward and downward.causing a function drive bail I2 coupled thereto by spring means 49. tolikewise experience a reciprocating or upward and downward movement.

The assembly of FIG. I is further provided with a carriage returnfunction lever 21 and a carriage backspace function lever 25, eachhaving their forward end supported by shaft 30. The levers 21 and 25pass beneath bail I2 and code bar assembly 27 so as to extend rearwardlywith their free ends being respectively aligned with a carriage returnfunction bail l9 and a carriage backspace function bail 23,respectively, so as to be aligned substantially coplanar therewith.

Levers 21 and 25 are respectively biased to rock upwardly by springs 31and 32 which maintain the upper edges of these levers 21 and 25 incontact with the lower edge of bail 12.

A carriage drive bail 11 is positioned in front of the function drivebail 12, and is designed to be rocked back and forth by means of a cam(not shown). The function of carriage drive bail 11 is to operate theprinting mechanism (not shown) supported by carriage 28 and to drivepawl 5 through the action of a roller 8 secured to carriage drive bail11 by fastening means 8a so as to project downwardly in order to makeselective engagement with drive pawl 5 for the purpose of advancingratchet wheel 2 one tooth after another against the tension of spring 1,causing carriage 28 to be spaced in a step-by-step fashion toward theright, as shown by arrow B.

A print suppression code bar 26, shown mounted in spaced parallelfashion relative to the code bars of the bar group 27, is employed forthe purpose of suppressing or preventing a printing operation, and, atthe same time, for blocking carriage 28 from spacing (i.e. incrementallymoving) toward the right. When a character code is received, the printsupression code bar 26 moves upwardly and to the left, so as to unblockthe printing mechanism supported in the carriage 28, allowing theprinting mechanism to operate and thereby perform the printing function.As part of the printing operation and substantially immediately aftercompletion thereof, the carriage 28 moves one character space toward theright before a subsequent printing operation occurs. FIG. 3 illustratesthe manner in which the spacing mechanism operates to cause the carriage28 to move one space to the right.

Referring initially to FIG. 2, let it be assumed that a character codehas been received from the sending teleprinter. This causes the printsuppression code bar 26 to move upwardly and to the left causing itsleft-hand most end to strike extension 33provided on a space suppressionlatch 14. This causes space suppression latch 14 to rotatecounterclockwise about its pivot S and against the normal biasing forceof tension spring 48 coupled between space suppression latch I4 and asuitable portion of the teleprinter frame. Rotation of space suppressionlatch 14 counterclockwise about pivot 8;, from the position shown inFIG. 2 toward the position shown in FIG. 3 causes a shoulder 37 providedalong latch 14 to be rotated out of the path of movement of a projection36 provided on one edge of the spacing pawl 5 which will thereby enablethe toggle linkage comprised of feed pawl 5 and toggle link 9 to buckleor collapse at its knee in a manner to be more fully described.

During the moment at which the space suppression latch 14 unlatches theprojection 36 on feed pawl 5, the carriage drive bail 11 (See FIG. I) isin the midst of the first half of its function cycle and is swingingrearwardly causing its associated roller 8 to likewise swing rearwardly.This enables toggle link 9, which is normally biased by spring means 9a,to rotate in a clockwise direction about pivot pin 35 so as to followthe rearward movement of roller 8. This causes the right-hand endsoffeed pawl 5 and backspace pawl 4, which are both rotatably mounted totoggle link 9 through pivot pin P,, to rotate counterclockwise from theposition shown in FIG. 2 toward the position shown in FIG. 3. In otherwords, the toggle linkage comprised of feed pawl 5 and toggle link 9 iscaused to buckle or break at the knee, collapsing the toggle linkage anddriving the pawls 4 and 5 from a first tooth 2a, as shown in FIG 2, intoa position of engagement with the next tooth 2c, as shown in FIG. 3, thesaid next tooth being to the right relative to the tooth 2a from whichthe pawls 4 and 5 have been removed.

The check pawl 6, which is pivotally mounted upon pin 35 together withtoggle link 9, remains in engagement with the preceding notch (i.e.,tooth 2a) of ratchet wheel 2 in spite of the rearward movement of roller8, since the check pawl 6 is a straight rigid member and is unaffectedby the rearward movement of roller 8.

FIGS. 2a and 3a show the diagrammatic representations to indicate thestepping operation. Before movement of roller 8 in the rearwarddirection (and assuming movement of shoulder 37 out of the path ofmotion of projection 36) all three pawls 4-6 are contained within notch20 with pawl 5 having its left-hand most edge abutting against theshoulder-2b (FIG 2a). With the rearward movement of roller 8, pawls 4and 5 are withdrawn from notch 2a and move into notch 20 while someminor movement is experienced by ratchet 2, check pawl 6 neverthelessrestrains ratchet 2 from moving a full incremental angle toward theright (i.e., counter clockwise). The forward movement of roller 8 causesthe toggle assembly to move from the collapsed position of FIG. 3-

toward the extended position of FIG. 2 which drives pawls 4 and 5 towardthe left relative to FIG. 3 and hence toward the position shown in FIG.2. This drives the ratchet 2 toward the left (i.e., clockwise) toadvance carriage assembly 28 one space toward the right. In actuality,in moving from the diagrammatic position of FIG. 3 to the position ofFIG. 2, all three pawls 4-6 would actually rest within a notch 20.

Of the two pawls 4 and 5, it can be seen that feed pawl 5 extendsslightly more toward the left than pawl 4, causing feed.

pawl 5 to operate as the stepping pawl in the performance of a steppingor spacing operation. The check pawl 6, inbeing restored to the stateillustrated in F IG. 2, in actuality, climbs over the tooth adjacent thenotch 20 to which the feed pawl 5 has been engaged and urges the ratchet2 toward the left (Le. clockwise) against the tension of spring 1. Thismotion causes the sprocket, SP mounted upon ratchet shaft 8, to move toan angle equivalent to one tooth pitch thereby causing carriage 28 tomove one character or space toward the right.

When a function code is received, a corresponding function lever, forexample, carriage return function lever 21, is selectively operated sothat a projection (not shown) provided on the underside of printsuppression code bar 26 strikes the side of the carriage return functionlever 21 which causes the code bar 26 to be blocked from moving upwardand to the left as previously described and hence causes the printingoperation to be blocked. This results in the space suppression latch 14remaining in the stationary or rest position of FIG. 2. Therefore,notwithstanding the fact that the carriage drive ball 1 1 is rockedrearwardly, the projection 36 on the feed pawl 5 is caused to remainengaged with the notch 37 provided on space suppression latch 14 so asto block the toggle link 9 from following the movement of roller 8beyond some slight movement. This blocks the toggle link 9 from rotatingclockwise about pivot pin 35, preventing the feed pawl 5 and backspacepawl 4 from falling into the next notch and hence preventing theprinting carriage 28 from spacing one incremental step toward the right.The actual movement of the toggle link 9 before projection 36 strikesshoulder 37 is only a fraction of one tooth pitch D (See FIG. 4a) sothat the movement of pawls 4 and 5 is so slight as to prevent theratchet 2 from advancing beyond the notch 2a, shown in FIG. 4. In otherwords, the carriage 28 is thereby placed in a space suppression state.

On receipt of a carriage return code, the carriage return function lever21 is enabled to be raised so as to follow the upward movement of bail12 by having its upper edge in contact with the lower edge of bail 12due to the biasing force of spring 31 coupled between lever 21 and bail12. The free forward most end of lever 21 falls into the notch providedin carriage return function bail 19. The upward movement of the carriagereturn function lever 21 blocks the print suppression code bar 26 frommoving upward and to the left with the result that the spacing of theprinting carriage 28 is blocked in a manner substantially identical tothat previously described.

The downward movement of the function drive bail I2 urges the carriagereturn function lever 21 to be rocked downwardly which, in turn, drivesthe carriage return function bail l9 downwardly against the biasingforce of tension spring 38 coupled between an upward projection of baill9 and stationary portion of the teleprinter frame.

The vertically downward movement of bail 19 is imparted to the free endof lever 20 as a result of the flange 39 which engages and drives lever20 downwardly. The opposite end of lever 20 is rotatably mounted onshaft 30. The downward rocking movement experienced by lever 20 isimparted to a bell crank 16 pivotally mounted upon a pin 40 by means ofa downward projection 20a provided along the lower edge of lever 20intermediate the ends thereof which abuts a projection 16b provided onthe bell crank assembly 16. This causes the bell crank assembly 16 torotate about its pivot pin 40 in a counterclockwise direction. Therotation of bell crank 16 is imparted to a connecting link pivotallycoupled to bell crank 16 and the lever 41 by pins 16a and 41arespectively. The substantially rearward linear movement experienced byconnecting link 15 causes lever 41 to turn counterclockwise about pivotpin 35. This results from the fact that the end of lever 41 is clamped(by fastening means 42a) to the free end 42 of lever 3, which ispivotally connected to pin 35 and has a release plate 43 at its oppositeend. Thus, the rearward movement of link 15 causes lever 3 to turncounterclockwise about pivot 35 together with lever 41, as shown byarrow C.

The left-hand end of lever 3 forms a release plate 43 which is situatedbetween the extension provided on pawls 46 and the spacing ratchet 2.Thus, as lever 3 is turned counterclockwise, as shown by arrow C,release plate 43 moves from its rest or dotted line position as shown inFIG. 5 toward the solid line position of FIG. 5, causing the feed pawl 5and check pawl 6 (normally, biased toward ratchet wheel 2 by springs 5band 6b, respectively) to be released from ratchet wheel 2 in succession,followed ultimately by the release of backspace pawl 4. Under suchconditions, the ratchet wheel 2 is free from any restraint whatsoever,placing carriage 28 completely under the control of the spring tensionof spring 1 thereby causing it to be rapidly returned to the left marginas a result of this spring force. Although not shown in the diagrammaticview of FIGS. 5 and 5a, it should be obvious that the release plate 43moves an amount sufficient to release pawl 4 from the ratchet 2 as wellas pawls 5 and 6.

Lever 3 is further provided with a downwardly extending projection 47which, when the carriage return function lever 21 rocks to its lowestposition, is caused to drop into a notch 46 provided in latch 7positioned beneath the release plate 43 so as to remain locked in thisposition until the printing carriage 28 is fully restored to theleft-hand margin.

The backspacing mechanism of the instant invention is designed so thatthe carriage return operation may be performed by one character pitch orspacing each time a backspaced code is received. In order to attain thisobjective, a backspace pawl 4 is provided upon a pivot shaft P as shownin FIGS. 26 to cause feed pawl 5 to undergo slight linear displacementin a manner to be more fully described.

Referring to FIG. 1, when any code other than a backspace code isreceived, the lifting operation of the backspace function lever 25 isblocked by a downward projection provided on at least one code bar ofthe bar group 27 (Sec FIG. 7) whereas, when the backspace code isreceived all code bars of bar group 27 are lifted and the backspacefunction lever 25 is free to rise without being impeded by the downwardprojection of any of the code bars of bar group 27 and thereby is liftedtogether with the bail 12 so as to follow the lifting operation of bail12 through the spring connecting means 32.

FIG. 7 shows the position of the code bars of bar group 27 when any codeother than a backspace code is received. As can clearly be seen, one ormore of the code bars of bar group 27 is in a downward position blockingany upward movement of backspace function lever 25 under control of thespring means 32 coupled between lever 25 and bail 12. When a backspacecode is received, all of the code bars of bar group 27 are liftedpermitting the lever 25 to lift under control of the rocking of bail I2,as shown best in FIG. 8. The left-hand end of lever 25 as shown in FIG.8 falls into a notch 23a provided in the carriage backspace functionbail 23. This lifting operation places lever 25 in the path of movementof the print suppression code bar 26, as can best be seen in FIG. 8, toprevent bar 26 from shifting upward and to the left (i.e., verticallyupward and out of the plane of FIG. 8), which is the movement undertakenby bar 26 when a carriage return code is received. Thus, the spacing ofcarriage 28, as well as the carriage return operation is therebysuppressed.

After bail 12 rocks to its highest level, it then moves downwardlycausing lever 25 to be urged downwardly as well. The left-hand end oflever 25, being positioned in notch 23a, urges the backspace functionbail 23 downwardly against the tension of spring means 38a. The downwardvertical movement of bail 23 is imparted to lever 24 by means of flange45 provided on bail 23 which bears against the upper edge of theleft-hand most end of lever 24. The forward end of lever 24 is rotatablymounted on shaft 30 causing lever 24 to pivot about shaft 30. Lever 24is provided with a downwardly depending projection 24a intermediate theends of the lever 24 which is caused to make engagement with aprojection 18a on bell crank 18 (See also FIG. 1), driving bell crank 18to turn counterclockwise about shaft 40. The rotation of bell crank 18is imparted to plate 17 which is clamped to the left-hand side of thebell crank 18 and which is mounted to pivot about pin 40. Plate 17 isprovided with a transversly extending elongated projection 51 which,upon rotation of plate 17, is urged against bell crank 16 to drive itinto counterclockwise rotation about shaft 40.

The function performed by bell crank 16 is normally associated with thecarriage return operation. Thus, the link 15 moves rearwardly and thelever 3 provided with the release plate 43 is caused to turncounterclockwise about the pivot pin 35 in the same manner as waspreviously described with respect to the carriage return operation so asto release both the feed pawl 5 and the check pawl 6 by means of therelease plate 43. The ratchet wheel 2 which has been engaged by the feedpawl 5 and the check pawl 6 with the relative positions as shown inFIGS. 4 and 4a, is permitted to be reversibly rotated through a nominalangle until the backspace pawl 4 completely engages the ratchet notch 2awith which the check pawl 6 was previously engaged, in a manner as canbest be seen in FIG. 5, as a result of the release plate 43 releasingthe feed pawl 5 and the check pawl 6 from engagement with the ratchet 2.The motion of ratchet wheel 2 is converted into linear motion of thecarriage 28 to retract at a small distance toward the left, i.e., adistance toward the left nearly equal to one space. If the backspacepawl 4 were desired to be released from the ratchet 2 by release plate43, the carriage 28 would be immediately restored to the left margin. Toprevent such undesired operation (when receiving a backspace code), thefollowing mechanism has been incorporated as part of the backspacingoperation:

Considering any of the FIGS. 26 and 2a6a, it can be seen that each ofthe pawls 46 are provided with extensions each having an engaging edge4a--6a, respectively, which edges are designed to be selectively engagedby release plate 43. When the pawls 46 are in their rest position, asshown in FIGS. 2 and 2a, it can clearly be seen that the edge 4a isfurthest removed from the edges 5a and 6a which are substantiallycoplanar when in the rest position. With this arrangement, movement ofthe release plate 43 from the dotted line position of FIG. 5 toward thesolid line position of FIG. 5 will cause the release plate 43 to firstengage the edges 5a and 6a to first release pawls 5 and 6 from ratchet 2and to finally release pawl 4 from ratchet 2 through the engagement ofrelease plate 43 with the edge 4a. However, the release operationperformed by release plate 43 must be such that movement of releaseplate 43 will be interrupted prior to the release of backspacing pawl 4from ratchet 2 and subsequent to the release of pawls 5 and 6 fromratchet 2.

The timing of this interruption is carried out by the backspace functionbail 23 in the following manner:

The lowermost edge of the backspace function pawl 23 is formed toprovide a slanted or diagonal surface 52 for cooperative engagement withroller 22. As the bail 23 is driven downwardly against the tension ofspring 38a and under control of lever 25, the slant surface 52 slidinglyengages roller 22 causing the bail 23 to be tilted rearwardly (i.e.,toward the left, as is shown in FIG. 9) as it moves downwardly.

When a backspace code is received all of the code bars of bar group 27are lifted upwardly to the position shown in FIG. 8. Lever 25 followsthe lifting of bail 12 as a result of the spring 32 coupling theelements 12 and 25. The lifting of lever 25 causes its free end(left-hand end relative to FIGS. 710) to enter the notch 230 provided inbail 23.

After bail 12 reaches its topmost position, it then rocks downwardlyfrom the position shown in FIG. 8 toward the position shown in FIG. 9 soas to drive lever 25 downwardly carrying with it bail 23. The flange-45provided on bail 23 drives the left-hand most end of lever 24 downwardlywhich, in turn, causes projection 24a to operate the bell crankprojection 18a in the same manner as was previously described.

As the downward movement of bail 23 continues under control of lever 25,its slant surface 52 engages roller 22 caus' ing bail 23 to move towardthe left as it moves downwardly. The leftward movement or tiltingmovement of bail 23 as its slant surface 52 slidingly engages roller 22causes the forward edge of lever 25 to be lifted out of notch 23a, asshown in FIG. 9, so as to abruptly discontinue the lowering movement ofbail 23 at a predetermined moment. The bail 23 immediately movesupwardly under control of the tension spring 38a from the' positionshown in FIG. 9 toward the position shown in FIG. 8; This abruptlydiscontinues the lowering operation of lever 24 under control of theprojection 45 of bail 23 so as to suspend the release operation ofrelease plate 43 prior to the release of backspace pawl 4 from ratchetwheel 2. The exact moment of interruption of release plate 43 iscontrolled by the relative positions of bail 23 and roller 22 and by theslant angle of slant surface 52:

Interruption of the rotational movement of lever 3 which carries releaseplate 43, prior to the release of the backspace pawl 4 from the ratchetwheel 2, indicates that the interruption occurs prior to the'time atwhich the extension 47 also carried by lever 3 falls into the notch 46provided in latch 7. Thus, the lever 3 initiates the return stroke whichrestores the lever 3 to its initial position as well as restoring thebackspace function bail 23, the backspace function lever 25 and thebackspace drive lever 24 to their original positions, as shown in FIG.10. By restoring lever 3 with its release plate 43 to its initialposition, both the feed pawl 5 and the check pawl 6 which have beenpreviously released, fall into a notch adjacent the notch with which thebackspace pawl 4 is engaged, as is il lustrated in FIGS. 6 and 6a.

The carriage drive bail II which is executing a returning stroke by thistime, begins to rock frontwardly. Roller 8 coupled to bail II by shaft8a urges the toggle link 9 counterclockwise from the position shown inFIG. 6 to restore it to its original position so as to move it from theposition shown in FIG. 6 toward the position of FIG. I. At thecompletion of the return stroke of carriage bail II, the right-hand end4b of backspacing pawl 4 strikes the forward edge of a recessed arm Ifixed on the frame of the device which exerts pressure thereon so as torotate pawl 4 slightly counterclockwise about its pivot I so as torelease the backspacing pawl 4 from ratchet 2 while it is in the normalor rest position. As soon as the pawl 4 is released from engaging anotch in the ratchet 2, ratchet wheel 2 retrogresses until the feed pawlwhich has already come into contact with a tooth flank surface reachesthe bottom ofa notch.

Thus, the carriage 28 is caused to backspace through one character spacein a simple and yet very accurate manner. The backspacing occurs as manytimes as backspace codes are received.

Briefly summarizing a backspacing operation:

Rest position is shown in FIG. 2. The pawl 5 furthest removed from pivotpin 35 engages notch surface 2b. Roller 8 moves toward the rear. Notch37 is in the path of projection 36 preventing toggle links 5 and 9 fromcollapsing (See FIG. 4). Toggle links 5 and 9 however, do break slightlyto permit pawl 4 to enter into notch 2a. Release plate 43 moves from theposition of FIG. 4 to the position of FIG. 5 to release pawls 5 and 6from ratchet 2. Pawl 4 then engages notch surface 2b (ratchet movesnearly through one space). Release plate 43 returns from the (solidline) position of FIG. 5 to the position of FIG. 6 causing pawls 5 and 6to enter notch 2d to the leftof notch 20. Roller 8 moves toward thefront again lifting pawl 4 out ofengagement with the ratchet 2 (See FIG.2) to complete backspacing operation. At this time pawl 5 restrainsratchet 2.

In accordance with the backspacing mechanism of the instant invention,only a backspacing pawl 4, which is extremely simple in construction, isincorporated into a conventional spacing mechanism in such a manner thatrotational movement of the already existing release plate 43 may beutilized for the backspacing operation and further that the carriagereturn operation may not be blocked. In addition, a

mechanism substantially similar to the conventional carriagev returnfunction mechanism may be employed as the mechanism for detecting thereceive backspace code and driving the release plate 43 towardthebackspace pawl 4 by an amount sufficient to perform the backspacingoperation and, yet insufficient to perform a carriage return operation.

In conclusion, the instant invention can be seen to provide a great dealof utility in providing a carriage backspacing,

mechanism featured by a reliability of operation and economy in numberof components employed and the ease of manufacture, installation andoperation.

We claim:

I.' In a teleprinter assembly comprising a printing carriage assemblyincluding:

a rotatable member; spring means for normally biasing said carriageassembly in a reverse direction; a spacing mechanism selectivelyengaging said rotatable member for advancing said carriage assemblyagainst said spring means one space in a forward direction responsive toa space or character code; a carriage return mechanism responsive to acarriage return code for releasing said spacing mechanism from saidcarriage assembly rotatable member to place said carriage assembly undercontrol of said spring means; the improvement comprising:

backspacing means coupled to said spacing mechanism and selectivelyengaging said rotatable member for enabling backspacing of said carriageassembly in said reverse direction by only one space responsive to eachbackspace code;

said backspacing means further comprising means coupled to said carriagereturn mechanism to release only said spacing mechanism from saidcarriage assembly drive member during a backspacing operation and torelease both said spacing mechanism and, said backspacing means during acarriage return operation;

said carriage assembly being comprised of a carriage;

a belt entrained about rotatably mounted driving and driven pulleys;

said carriage being secured to said belt at a point between saidpulleys;

said rotatable member being a ratchet wheel, a shaft coupling saidratchet wheel to said driving pulley;

said spring means being coupled to said carriage for normally urgingsaid carriage in a reverse direction;

said spacing mechanism comprising; a pivotally mounted check pawl and afeed pawl;

said feed pawl being provided at one end of a collapsible toggleassembly having a pivotally coupled knee portion;

bias means normally urging said pawls into engagement with said ratchetwheel;

first reciprocating drive means engaging said toggle assembly adjacentsaid knee portion to alternately collapse and extend said toggleassembly during a spacing operation to cause said feed pawl to advancesaid ratchet wheel by one tooth for each reciprocating cycle completedby said drive means; and

said backspacing means further including a backspacing pawl beingpivotally coupled to said toggle assembly knee portion.

2. The device of claim 1 wherein said carriage return mechanism iscomprised of a rockably mounted release plate;

each of said check, spacing and backspacing pawls having an extensionprojecting beyond said pawls;

said release plate being mounted to rock between said ratchet wheel andsaid extensions; and

the extension of said backspacing pawl being further removed from saidrelease plate than said spacing and check pawl extensions to cause saidbackspacing pawl to be the last pawl to be disengaged from said ratchetby the rocking of said release plate.

3. The device of claim 2 further comprising means for normallymaintaining said backspacing pawl from said ratchet wheel when saidspacing mechanism is in its rest position.

4. The device of claim 2 further comprising means for preventing thecollapse of said toggle assembly during either a carriage return or abackspacing operation.

5. The device of claim 4 wherein said backspacing means is furthercomprised of control means coupled to said rockable release plate;second reciprocating drive means for driving said control means forcontrolling the amount of travel of said release plate and therebypreventing said release plate from disengaging said backspacing pawlfrom said ratchet wheel during a backspacing operation.

6. The device of claim 5 wherein said release plate control means iscomprised of a rockable backspacing function lever operative to belifted and lowered upon the occurrence of a backspacing operation;

a backspacing function bail having a notch engageable with said functionlever as said function lever is lifted;

said function bail being biased in a first direction to be normallylifted;

the lowering of said function lever urging said backspacing functionbail in a second direction to lower said function bail; and

second lever means coupled to said release plate and engaged by saidfunction bail as it lowers for rocking said release plate.

7. The device of claim 6 further comprising stationary means positionedin the path of lowering movement of said function bail; and saidfunction bail having a slant surface confronting said stationary meansto disengage said function bail from said function lever to interruptthe rocking motion of said release plate prior to striking saidbackspacing pawl extension during a backspacing operation.

8. The device of claim 6 further comprising spring means coupling saidsecond reciprocating drive means to said function lever; and liftablecharacter code bar means selectively lifted upon receipt of a characteror spacing code and unanimously lifted upon receipt of a backspacingcode to enable said function lever to follow the lifting and loweringmovement of said second reciprocating drive means.

9. The device of claim 8 further comprising a carriage return code barliftable upon receipt of a carriage return code;

and said function lever normally blocking the lifting movement of saidcarriage return code bar when prevented from following the movement ofsaid second reciprocating drive means by at least one of said charactercode bar means.

